1. Field of the Invention
This invention relates in general to screen printing frames and stretchers and in particular to screen printing frames and stretchers for use with bordered fabric.
2. Prior Art
In screen printing it is desirable to have screens that can be quickly and easily stretched. Once a screen has been initially stretched, it is desirable to be able to quickly increase the tension of the screen as it inevitably loses tension with time and to adjust an imaged screen so that coordinates of the imaged screen can be moved in relation to the coordinates of a substrate on a printing press.
The earliest frames were simple wooden or metal rigid frames on which the fabric was stapled or glued as the fabric was stretched by hand or by mechanical means. Later, frames evolved wherein the fabric could be fastened to the frame sides and by rolling, telescoping, or expanding the sides of the frame, the fabric could be stretched. The stretching process became internal to the frame rather than external to the frame. Notable examples of self-tensioning screen frames of this type include U.S. Pat. No. 3,482,343 by Hamu, U.S. Pat. No. 3,914,887 by Don Newman, and U.S. Pat. No. 5,113,611 by Gene Rosson. These screen frames, in eliminating the use of external stretcher devices, do not have all the advantages offered by some external stretching systems. For example, pneumatic clamp and stretch systems have been developed which can very accurately distribute uniform tension over the entire area of a screen. Self tensioning screens, on the other hand, generally have greater tension in the corner areas. Hamu's draw-bar frame is able to overcome this problem but it is a difficult and labor intensive frame to work with. Also, the Hamu frame, unless made extremely bulky and oversized, has a limited stretch distance that is inadequate for many highly stretchable fabrics.
Bordered fabric and frames were introduced in U.S. Pat. No. 3,991,677 by V. H. Barnes, U.S. Pat. No. 3,211,089 by Edgar Messerschmidt, U.S. Pat. No. 3,416,445 by T. H. Krueger, U.S. Pat. No. 2,903,967 by H. S. Levin, U.S. Pat. No. 3,078,793 by D. Jaffa, U.S. Pat. No. 5,274,934 by Eugene Newman, and U.S. Pat. No. 5,390,596 by Gregory Farr. Eugene Newman discusses using an external stretching device to attach bordered fabric to a frame. This is the only reference in the prior art to an external stretcher device used to stretch bordered fabric onto a frame. All other prior art refers to self-tensioning frames. In U.S. Pat. No. 5,522,314, Eugene Newman further teaches a method of constructing border strips onto fabric so as to embody the bordered fabric, when stretched, with an accurate and uniform tension level throughout the screen.
In practice, the use of an external stretcher device to stretch and mount a piece of bordered fabric to a rigid frame as taught by Eugene Newman in U.S. Pat. No. 5,274,934 is a quick and easy way to stretch a screen initially. However, re-tensioning continues to rely upon a stretcher device that must be attached directly to the border strips. Adapters, used as spacers, are inserted between the outwardly pulled border strips and the outside walls of the frame, filling in the gaps left by the outward pulling of the border strips away from the frame. These adapters are awkward to work with and limit re-tensioning to discreet increments rather than a continuous range. Also, by teaching that the external stretcher device always attaches to the border strips, other means of re-tensioning the screen are not explored.
Whatever the precise merits, features, and advantages of the above cited references, none of them achieves or fulfills the purposes of the present invention.